Here I am going to go through the repair of this Issue 7 Model Beeb that I picked up eBay. It was sold as non-working and making a continuous beep/wail when powered on. One of the main things that dog the BBC Model B is a couple of Capacitors on the PSU. There are a couple of X2 Capacitors and a normal electrolytic capacitor too. These are the main three and that cause problems and should be replaced in any event. If you see something along the lines of " turned it on, there was a pop and a burning smell " these are what have blown in most cases.
In this case there was no improvement which was a bit frustrating. So I started to check the voltages on the board and they are all fine so the power was OK. I tried the minimal boot configuration with all non-essential chips removed and setting the jumper that controls the RAM available in all three combinations ( Bank 0, Bank 1 and Bank 0 + 1 so 16KB, 16KB and 32KB )
Still made no headway so pressed the Break key which is a soft reset button and the BBC booted, I connected it to a TV to check and was greeted with the BBC 32K message follwed by Language? which means it could not see the BASIC ROM.
I was testing it further and power cycled the machine and then it went back to the long wailing beep So having checked some of the custom IC's I turned to the logic IC's, using the schematic I identified the logic chips that control the BASIC and OS 1.2 access and started to remove them, test them, fit a Dip socket and if they passed the were fitted back into the machine. This is how I found the 74LS139 chip was faulty and having it fail could cause the problem. So hopefully it will cure the problem when I get some.
In the meantime just for Baker here is a picture of inside a 32K BBC - talk about "real estate" there are an awful lot of chips on this board and one thing I am not a fan of is the vertically mounted resistors....
Is exactly the same prompt that old Diablo68 gets with his Beeb too.
I was thinking he needed the BASIC ROM stuck in one of the x5 ROM chip slots pictured bottom left in your image...
It might though be a bit more problematic than that and perhaps he has logic chips gone on his motherboard too?
Any road, your logic chips are, as far as I know, on their way over to the Baz Biome, mate.
Will keep you up to date and then get a package to you next week featuring - Beeb logic chips, Speccy Microdrive AND a few Chinese solar lights...
AS YOU DO!!!
Yeah 8bitbaz you need the BASIC ROM in there else you get the "Language?" prompt. You normally have in the last slot after any EPROMS fitted or in the case of this one right after the OS as there are no EPROM's. If there is no BASIC ( see IC 52 for chip info ) in the machine then it sounds like the Beeb used to have a sideways ROM/RAM board that has since been removed and the BASIC not fitted back onto the motherboard or someone just removed it.
Well as a follow on from the last real post I made about the Beeb and it giving the Language? prompt. This gradually progressed to the Beeb refusing to POST at all. I had gone backwards it seems and I was worried it was something I had done or the one of the more hard to find IC's had failed. So I needed to have a more methodical approach with this one.
So I got hold of the schematic for a BBC and with the help and advice of the guys on stardot I was able to discount the RAM as setting the jumper for each 16K RAM bank showed no RAM errors. The 6522’s and 6502a were OK. The Mask ROMs were advised to be very unlikely to be faulty. So looking at the schematic IC 20 and IC 26 which were both 74ls139’s so I desoldered them and tested them in my EPROM programmer and one had failed. Replaced the faulty ls139 and tried it again and greeted with the normal Bee-Boop and BBC 32K BASIC >
Now I have a working Beeb I have a few upgrades coming or already here to pimp it out a bit. I didn't realise it was this expandable! So I have already fitted a 1770 DFS Board and ROM. So now it is floppy drive ready. I have a Gotek Drive on its way to me now, along with a ATPL Sidewise board. The Sidewise is a Sideways ROM/RAM board and the one that is coming already has 16KB of RAM fitted. The reason I bring that up is this board needs the jumpers changing so if they were not fitted back that would definitely cause the symptoms you describe.
I also have a Raspberry Pi Co-Processor board as well so I can now play the Co-Pro Elite! The Pi allows you to have various Co-Pro Cores ( 65c02, Z80, 6809, 80286 and Arm ) with speeds of around 150Mhz or more so should be interesting to see what it's like.
I now have the ATPL Sidewise ROM/RAM Board fitted which allows all 16 ROM or 15+1 ROM-RAM Slots to be filled ( currently has 16KB of Sideways RAM fitted ) in addition to the 1770 Disk Drive PCB I already purchased and have also picked up a Watford Electronics 32KB Shadow RAM board off feeBay for £11. Finally I have a Gotek USB floppy drive for it as well. So I think I have pimped this Beeb enough for now... Time to enjoy some Co-Pro Elite Executive Edition and see what else it can do.
I have to admit 8bitbaz that I always thought the Beeb wasn’t that good. That was based on my experience in the 1980’s though, using them in school and also my friends gaff. It always seemed too low on memory.If you use Mode 0 for example, that uses 20K of RAM for the screen so doesn’t leave much room for actual code. That opinion was based on an unexpanded model though, so having said that I have been surprised how much you can add to the Beeb and how advanced the BASIC is, in addition to the other options like the Econet networking capabilities, so my opinion has changed a bit since this arrived on my workbench Just goes to show I guess.